Often in the world of marketing, you will come across the terms on-
On page optimisation is essentially making changes on a page or pages within your website or by adding new content to your existing site. It may be that you add a blog or that you optimisation the content on a page in include more keywords. On page optimisation also includes adding internal links to other pages and adding meta date, adding XML site maps and internal linking to relevant pages. It may also include changing the way your URL’s are displayed and ensuring there are no broken links.
Off page or marketing is something that you do off your website that is aimed at improving the traffic to your site and your rankings on the search engines. This may be building up external links to your site by getting links from other quality websites or directories, guessed blogging on other sites, social media interaction and uploading videos through YouTube that relate to your website. All of these can influenced your website positively.